Two Orcas' Taste for Shark Liver Upends Entire Ecosystem

“The Butterfly Effect,” is a term for a small change in one place (like the beating of a butterfly’s wings) that leads, step-by-step, to major changes elsewhere. It seems it could also be called the “Orca Effect” thanks to the strange hunting patterns of a pair of killer whales off the coast of South Africa. 

A pair of Orcas prowl the waters along South Africa’s Western Cape. They are nicknamed Port and Starboard for the way their dorsal fins droop to the left and right. The pair hunt for a very specific meal. They eat the livers of great white sharks.   

The orcas have worked together with their podmates to kill perhaps a dozen or more great whites in the region over the past 10 years. Their strikes are precise. Marine biologists have found a number of dead sharks where only the liver has been bitten out.  

Once home to more than 1,000 great whites, the region's ecosystem is now much changed. The sharks have been repeatedly driven off. Some disappear for years at a time. That’s allowed the population of their primary prey, the cape fur seal, to explode. In turn, some of the seals have begun to feed on the critically endangered African penguins in the area, biologist Alison Towner told the Guardian. She has been counting the shark deaths. The lack of sharks has also allowed rabies to spread among seals. Rabies is a dangerous disease. It could threaten humans in the area.    

“In my opinion, if white shark populations were at their previous peak, they might have helped mitigate the rabies situation," expert Esther Jacobs told The Guardian. "Rabid seals would likely be easier targets."    

Reflect: How can small changes in one part of an ecosystem affect the rest of the environment?

Gif of orca whales from GIPHY.